This invention is related to fluid control system pilot valves which sense a pressure in a system and control the flow of fluid to some pressure actuated device in the event the sensed pressure rises above or drops below predetermined values.
Several pilot values are known in the art which will perform a generally similar function to the pilot valve of this invention. As an example of the known patented prior art pilot valve structures, reference is made to U.S. Pat. Nos. 3,621,881, dated Nov. 23, 1971; 3,716,074, dated Feb. 13, 1973; and 3,863,672, dated Feb. 4, 1975.
Such prior art combination high-low pressure responsive pilot valve mechanisms have a relatively large dead band or range of intermediate pressures which are not sufficiently high or low to actuate the mechanism thus making it undesirable for situations requiring fine control through a narrow range of pressures. Further, the rate of bleeding or exhausting an associated valve actuator has been relatively slow which further makes such prior art pilot valve mechanisms undesirable. When only a pilot valve is employed for bleeding an associated valve actuator to permit a controlled valve to close or shut in, it is highly desirable that a fast rate of exhausting the actuator be obtained so that associated valve will move to a closed position in a minimum of time.
In addition, the prior art arrangements have utilized the outlet port of the pilot valve mechanism for bleeding off the valve actuator under both high pressure and low pressure conditions. The outlet port heretofore has been of a relatively small cross-sectional area to permit a fluid seal to easily move across the outlet port for bleeding the actuator under both low pressure and high pressure conditions. Thus, the size of the outlet port has controlled the rate of bleed off of the fluid from the actuator when pilot valves have been utilized for bleeding valve actuators.